Posted
by
samzenpus
on Wednesday July 27, 2011 @02:51PM
from the little-brother dept.

The Bad Astronomer writes "Astronomers have found the very first Earth Trojan asteroid, a rock that more-or-less shares Earth's orbit around the Sun. Seen in data by NASA's WISE mission, 2010 TK7 is about 300 meters across and leads the Earth by 60 degrees around the Sun. Trojans have been seen for Jupiter, Neptune, and Mars, but this is the first for our planet."

yes but the sun would also give a glair on any ground-based telescopes...

Where would the Sun get egg whites?

If you mean glare, you'd be wrong. Astronomical darkness ends about an hour and a quarter before sunrise. This asteroid, because of its orbit, will rise precisely four hours before the sun. So you've got over 2.5 hours of dark in which it would be visible.

And here I thought that from what I've heard so far that Earth had possibly some dust or at most some gravel at its L4 and L5 points. This discovery of a sizable asteroid there makes the Earth's L4/L5 points much more interesting. Hopefully there is even more to be found!

Who will be the first person to suggest placing VLBI radio telescopes at each lagrange point? Oh I guess it'll be me. A nice heavy asteroid would be convenient for vibration dampening WRT antenna pointing.

The problem is when/if we ever do planetary colonization, those L points will be in high demand for planetary relay satellites, as no matter where any other planet is in its orbit relative to earth's orbit, at least one earth L point should be in view... so what do we want there, sensitive receivers or big ole transmitters? I'm guessing we'll have some kind of scientific "quiet hours" scheme where the scientists get the first second of every minute, first minute of every hour, and first hour of every day, of radio silence. Or maybe they'll just be screwed?

those L points will be in high demand for planetary relay satellites, as no matter where any other planet is in its orbit relative to earth's orbit, at least one earth L point should be in view... so what do we want there, sensitive receivers or big ole transmitters?

Or we could split them up: One Lagrange point for transmitters, one for receivers?

It's *almost* an equilateral triangle, if the earth's mass were totally negligible then it would be perfect e. triangle. Don't forget the earth-sun distance varies too, in elliptical orbit case you get lagrange area rather than point you get with circle.

Planet requirements:1. It needs to be in orbit around the Sun. (Check)2. It needs to have enough gravity to pull itself into a spherical shape. (Check)3. It needs to have “cleared the neighborhood” of its orbit. (Uh oh! Pluto doesn't satisfy this requirement and apparently now Earth doesn't either!)

Yes, jests are fun. But seriously, it would depend on how many decimal places before you agree to round up to "swept out". I think most people would be willing to round up in this case, but not in Pluto's.

That is because the IAU passed an IDIOTIC politically motivated definition defined by a committee of washed out has-been scientists, that made absolutely no sense neither scientifically nor in the lay vernacular.

By this definition- no extra-solar planet is actually a planet, since they don't orbit the Sun (aka Sol, OUR star). Why they couldn't replace "sun" with "parent star" or "primary graviationally bound star" is beyond me.- a dwarf planet is not a planet either. (They needed to use another name for wha

Since this trojan shows that the Earth hasn't cleared its orbit, does that mean that Earth is no longer considered a planet?

Being in a Lagrange point doesn't mean that the Earth hasn't cleared its orbit. Unless you want to argue that the presence of a moon means the Earth hasn't cleared its orbit. After all, the moon also roughly follows the orbit of the earth around the Sun.

Given that the barycenter's center of mass is within Earth itself, I'm happy to call it Earth's orbit for simplicity's sake. Come to think of it, the only planet or dwarf planet whose satellite is massive enough to place the barycenter outside of the planet itself is Pluto.

I suppose that the astronomy and astrophysics communities could further refine the definition of planet based not only on size, but on the location of mass relative to a satellite...

Agreed, I've come to think that Phobos and Deimos should be reclassified as gravitationally trapped debris or something along those lines.To qualify as a satellite, using volume percentages would be problematic in the realm of gas and ice giant planets, so maybe something along the lines of spherical shape would be the way to go.

The problem with the barycenter rule is that the Jupiter-Sun barycenter is outside the Sun. Do you delist it as a planet because it doesn't orbit the Sun, but a point outside the Sun?

What we really need to do is get rid of the idea that planets are going to be a short, enumerable list that elementary school students can memorize, and instead use it to mean any object, wherever it is, that's too small for its gravity to make it fuse but big enough to wind up in a round shape under its own gravity.

The problem is big and massive are two different things, and it depends on the material composition of the object. So we will end up with objects that are in hyrdostatic equilibrium that are smaller in diameter / size than other objects that are not. Take asteroid 4 Vesta for instance, it's larger in diameter than several objects that are in hydrostatic equilibrium, yet it is not itself. Also there are plenty of moons that are in hydrostaic equilibrium, according to your definition these would be planets

Contrary to overwhelming corroborating opinion, the sun, while not super massive, is not an "average star" - being more massive than about 80% of others. Look it up in a star catalog (instead of google)

"In the end stages of planet formation, a planet will have "cleared the neighbourhood" of its own orbital zone, meaning it has become gravitationally dominant, and there are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence. A large body which meets the other criteria for a planet but has not cleared its neighbourhood is classified as a dwarf planet. This includes Pluto, which shares its orbital neighbourhood with Kuiper belt objects such as the plutinos. The IAU's definition does not attach specific numbers or equations to this term, but all the planets have cleared their neighbourhoods to a much greater extent than any dwarf planet, or any candidate for dwarf planet."

Don't neglect the "gravitational dominance" aspect, which can be calculated using the Planetary Discriminant (also described on that page), and essentially subsumes the "comparable size" part. If there were other objects of comparable size, then these metrics would necessarily be much smaller.

No, the Lagrange points are stable garbage dumps for planets to put "small" things of 9% of its mass or less, the stuff stays there. It's one of the ways a planet clears its orbit.

Theoretically you are right. Practically, the orbit of TK7 is actually unstable. Because TK7 executes some Lissajous orbit around L4 and the Moon orbit is eccentric [wikipedia.org] (search for the "the case of the Earth-Moon system" in the linked page).